Springs and strip steel



Jan. 26, 1965 A. v. BERNSTEIN ETAL 3,167,308

SPRINGS AND STRIP STEEL.

Filed May 28, 1962 2 II I II INVENTORS 4 Axel Bernstein BY Oscar E. d ohcmsson Q a; %/m$,/p

ATTORNEYS United States Patent This invention relates to springs of the spiral type, such as main springs for watches and clocks. More in particular, the invention relates to such springs of the type wherein the delivery of power may be subject to variations because of friction between the contacting surfaces of the adjacent turns.

In springs of the above type made of steel or other metallic alloys in flat strip form, difliculty has been encountered because of relatively wide variations in the power or working force of the springs. Such variations result from the effects of friction between the contacting surfaces of adjacent turns or coils of a spring. That is, when a spring of this type is being wound or is unwinding the adjacent coils or turns rub against each other and friction between the moving surfaces tends to cause uneven relative movement. This is particularly true when a spring starts to unwind from its fully wound position, wherein the turns or coils are somewhat tight against each other. When the spring is used to operate a watch, clock, or an instrument, there may be very substantial variations in the effective torque or power of the spring and resultant movement of the driven elements, and such variations may interfer with the proper operation of the device. It has been common practice to apply a thin layer of oil on springs of this type, but that solution is not fully satisfactory. The oil tends to produce adhesion between contacting surfaces of the coils. Also, the oil causes difliculties because of its deterioration and the changes in its viscosity. There have been other proposals for reducing the friction and for overcoming the difliculties encountered with oil, but no fully satisfactory solution has been provided these problems.

An object of this invention is to provide improved springs, such as, the main springs for watches and clocks, spiral power springs and instrument springs. A further object is to provide an improved spring structure. A further object is to provide improved coatings for reducing the friction between surfaces as discussed above. Another object is to provide an improved mode of applying coatings of the above character. Another object is to apply an improved protective structure upon a strip of spring steel or the like. These and other objects will be in part obvious and in part pointed out below.

In the drawings:

FIGURE 1 is a view of a spring constituting one embodiment of the invention;

FIGURE 2 is a greatly enlarged sectional view of two adjacent coils or turns on the line 22 of FIGURE 1;

FIGURES 3 and 4 are sectional views similar to FIG- URE 2, but showing other embodiments of the invention; and,

FIGURE 5 is a somewhat schematic view showing one mode of coating the strip steel in accordance with the invention.

Referring to FIGURE 1 of the drawings, a spring is tightly wound upon a spindle 4 within a barrel 6. Spring 1 is formed of a strip 2 of steel which is rectangular in cross-section, and, in FIGURE 2, the two turns or coils of the spring represented are designated 2a and 2b, respectively. Tightly fused to the top surface 8 of strip 2 is a continuous strip 10 of Teflon, and a similar strip 12 as to present convex surfaces.

3,1513% Patented Jan. 26, 1965 is fused to the bottom surface 14. In the present disclosure it is understood that Teflon is a trademark identifying a brand of polytetrafluoroethane, which is of the polyhalogenoalkene group, and is a polyfluorocarbon. The invention contemplates that a polyhalogenoethene or polychlorotrifluoroethene may be used.

When the spring is in the tightly wound condition of FIGURE 1, the surfaces of the Teflon strips 10 and 12 on turns 2a and 2b, respectively, contact each other so that the metal surfaces 8 and 14 are held apart. Accordingly, the adjacent turns or coils slide with respect to each other without the objectionablefriction and other difficulties which are encountered when the spring is bare. Also, it has been found that the relatively narrow contact area between the Teflon strips 10 and 12 produces very satisfactory operation. The Teflon strips of FIGURE 2 are relatively flat so that they have parallel contacting surfaces. Hence, the turns or coils are caused to position themselves in parallel relationship throughout the entire spiral of the spring. In FIGURE 3 an identical spring is provided with strips 20 and 22 which are crowned so This reduces the width of the contact area very materially and permits great leeway in the attitude or relative parallel relationship between the adjacent turns. In the embodiment of FIG- URE 4, the spring is of the cross-curved type having one concave and convex face. The Teflon strips 24 and 26 are of the type of strips 10 and 12.

The strips of spring steel from which the springs of FIGURES l to 4 are formed are produced and processed as in the manufacture of springs without the Teflon coating. As represented in FIGURE 5, the coating operation is performed by drawing the continuous strip over a roll 30, down into a body of liquid 32 which is a solution containing small particles of Teflon dispersed in water, around a roll 34, and thence vertically from the body of the liquid and up through a vertical drying and curing oven 36. As strip 2 moves upwardly from the body of liquid, a quantity of the liquid is carried by the surfaces of the strip. While the liquid tends to adhere to entire surfaces of the strip, it has been found that the layer of liquid becomes thin on the edges of the strip, and'tends to accumulate in thick strips or streams at'the centers of the side faces of the strip. As the strip moves upwardly with the two continuous strips or streams of liquid on its side faces, the upward movement of the strip counteracts the tendency for the liquid to run back down the strip. The liquid contains a substantial quantity of water, and the entire strip is thoroughly wetted. However, as indicated above there is a tendency for the liquid to run off the edges of the strip.

The drying and curing oven 36 is a vertical tunnel having heating elements along its side walls so as to subject the upwardly moving strip and the liquid to rather intense heat. This causes the water to evaporate from the liquid so that it rapidly becomes a highly concentrated Teflon solution. As the solution becomes more concentrated and the cross-sectional area of each stream is reduced, it tends to draw together at the center of the side face of the strip. This drawing together results from the actions of cohesion and surface tension with respect to the solution and the adhesion of the solution to the surface of the strip. Hence, at the zone in the oven where the water has been evaporated, there remains a layer of Teflon at the center of each side face of the strip. The further heating fuses the particles of Teflon together and also fuses the Teflon to the strip. The resulting product is the strip of metal having two continuous ribs or strips of Teflon fused to the centers of its side faces. Due to the flowing of the solution from the edges of the strip, the completed product may have little or no Teflon coating at the edge portions of the strip. When strip 2 is narrow as in the draw-- ings, the edge portions constitute-a substantial percentage of the strip. However, for strips of greater width, the

latingthe various factors and'operating conditions, taking accordance with the invention is uniform longitudinally i and'transversely of the strip, even when the strip is as edge portions are correspondingly smaller portions of the total strip surface,*and the surface covered by the Teflon coatings may be a major portion of the total. strip surface. a

It has be'en'p'ointed out above that the Teflon deposit. or coating strips may have crowned or convex surfaces as r f .in FIGURE 3,01: it may have flat s'urfaces as in FIG- URES 1 and 2. This characteristic is controlled by reguw into consideration the following: (1): the width of the metal strip, (2) theconccntrationor relative amount of 1 Teflon dispersed in the solution, ;(3) the speed. of move-.,-

ment of the strip, (4) thepresence, ,ofotherconstituents;

in the solution, and (5) the rate of. heating to which the strip and the solution are subjected in oven.36-.

The solutionhas been referred toasa dispersion of V Teflon particles in water, but it, also includesja wetting I agent so as to insure rapid and thorough-wetting of'the metal surfaces}. The solution is subjected to agitation to maintain a uniformdispersionwithoutcausing objeciionable surface agitation asmight interfere with the desired coating of liquid on thestrip as it moves upwardly. The a uniform rate of movement of the strip, vertically com{ bined with the maintenance of other uniform conditions,- insures uniform coatings upon the two side faces of the I strip. 7

. In the illustrativeembodimennstrip 2 is .0476 inch wide and .0044 inch thick." The Teflon coatings 10 and 12 are 00012 inch thick and of the order of .016 inch wide. Strip 2isof stainless spring steel which has been formed by flattening a round wire.

Hence, thefinal strip a.

has parallel side faces and side edgeswhichv are semicylindrical in cross-section. The stainless spring steel from strip 2 is formed contains the following .07 to 20% carbon, not more than ;-1% nitrogen; 14 to 20% chrom-p ium; 7 to 12% nickel; .2 to 2% silicon; .4 to 2% manganese; notmore than-4% molybdenum; not more than 10% cobalt; and, the remainder,iron with the normally v -40 springsfrom strip 2 the I occurring impurities.

Duringthe manufacture of V a I springs are subjected to .heat treatments at temperatures ment the Teflon is not adversely affected and does not suffer any, deterioration. *Furthermore, extensive tests have shownthat there is no adverseeffectfrom aging or during normal use. Springs manufactured in accordance with the invention are characterized by producing higher torque and more uniform power than. similar springs which are lubricated in .a conventional manner. I The in-. vention provides very satisfactorylubrication between the spring 'coils and insures proper functioning throughout the entire life of the spring without additional lubrication or other servicing. 1 a

In general, theinvention 'contemplatesthat'the thickness of eachTeflon coating shall be of the order of from parallel side faces and rounded edges and which includes as'illustrative and not in wide as inch. It has been found that satisfactory com mercial springs'can be profi l cedwith such a coated strip where each of the Teiion coatingsis ofa-thickness of the .order of .000005 inch to ,00001 inch. -While the'inventionhas particular utility with stainless spring steel, it is 'also applicable'with other steelsand other metallic alloys.

As many possible embodimentsmay be made of the mechanical-features of the above-invention and as the art herein described might be varied in. various parts, all

without departing from the scope'of the invention,fit is to be -understood that all matter hereinabove set forth, or

shown in. the accompanying drawings is to be interpreted a limiting sense.

1. A spiral metal spring which has contactingsurfaces tending toicontact each other andproduce friction, ,and

1 a'Teflon coating strip of lesser width than the spring and positioned substantially concentrically with respect to the longitudinal vcenter 'line of one of, saidcontactingsurfaces and providing I an anti-friction ;surface which extends 7 throughout the longitudinal extent of said contacting surface, said coating strip having a thickness'of the. order 0f .000 05 to,.0O016 inch. r i 1 2. Aspring as described in claim 1 wherein said antifriction surface is substantially straight in a direction transyerse toflthe longitudinal extent iofsaid contacting surface I v v a A spring ;asdescribediii-claim 1 whereinsaid anti: tr ctio'nsurface is substantially convex ina direction transverseto the longitudinal extent of said contacting surface.

i 4.- .A spring as described in claim 1 wherein said spring is concavo-convex.

5 :A; spring 'as describedin claim '1 in which isformed by a strip of stainless spring steel havingsubstantially .a' secondTTefloncoating strip, saidcoating stripsbeing substantially identical and beingpositioned respectively along said side faces.

- 6.1 A flat strip of metal which is substantially wider H 'than'jt isthick and-which hasisubstantiall y parallel. side withinth range of 6609 to 930 F. Duringsuch treatfaces, ar1d a pair :of coating strips of lesser-width than the strip of metal of a material of thepolyhalogenoalkenc group extending respectively along the longitudinal center lines of said side faces andfused to'the-surfaces of the from other conditions to which the springs are subjected .rnetal soas to. provide anti-friction a surfaces which. ex-

tend substantially throughout the length of 'said strip of f metal," each of said coating strips having'a thickness of 1 to'10% of the thickness of the steel strip. For Watch and clock springs, where the steel; strip is of-the order of .002 inch to .01 inch in thickne'ss,'the. thickness of'the Teflon coating is of the order of .00005 to .00028 inch, preferably not more than .0001 to .0012 inch; For

springs of the orderof .01 to .02 inch in thickness, such as are used in clocks, film cameras and typewriters, the coating layer may be of the order of .00059 inchonmore in thickness.

It has been found that the Teflon coatingproduced in the order of .00005 to .00016 inch. 1

. 7. A flat strip of metal as described in claim 6 which is in the form of a spiral spring of'thetype used/for watches,

clocks and the like. I

References Cited in the file of this patent UNITED, STATES PATENTS 

1.A SPIRAL METAL SPRING WHICH HAS CONTACTING SURFACES TENDING TO CONTACT EACH OTHER AND PRODUCE FRICTION, AND A TEFLON COATING STRIP OF LESSER WIDTH THAN THE SPRING AND POSITIONED SUBSTANTIALLY CONCENTRICALLY WITH RESPECT TO THE LONGITUDINAL CENTER LINE OF ONE OF SAID CONTACTING SURFACES AND PROVIDING AN ANTI-FRICTION SURFACE WHICH EXTENDS THROUGHOUT THE LONGITUDINAL EXTEND OF SAID CONTACTING SURFACE, SAID COATING STRIP HAVING A THICKNESS OF THE ORDER OF .00005 TO .00016 INCH. 